Media streams are transmitted and stored over various networks and devices. In order to provide high resolution color images in an efficient manner the image must be dramatically compressed. Various methods for compressing and decoding media streams have emerged. A group of compression standards was developed by the Moving Picture Expert Group. These standards are known in the art as the MPEG family. Each MPEG standard defines a method for compressing and transmitting audio-visual information according to predefined timing schemes that allow displaying audio visual content embedded within media streams.
Raw video streams are provided to an MPEG encoder. A raw video stream is encoded by an MPEG encoder to provide a video elementary stream. Video and audio elementary streams may be multiplexed to provide a transport stream or a program stream. A single transport stream can include a single program or multiple programs. Each transport stream packet includes a header that includes multiple fields such as a program identifier (PID) field.
In addition to video streams, network providers allow end users to exchange data over the Hybrid Fiber Coax (HFC) network that is mainly used for downstream transmissions and an optional out-of-band network. DOCSIS is a well known standard for transmission of the data.
Transport streams (TS) can include a single program or a multiplex of different programs. The latter is known as Multiple Program Transport Stream (MPTS).
An TS also includes Program Specific Information (PSI) that describes the programs that form the MPTS and the elementary streams that belong to each program. The PSI is conveyed in packets that have a unique PID. The PSI includes, for example, a Program Association Table (PAT) and a Program Map Table (PMT). The PAT lists the programs that are included within the TS and the PMT lists the various elementary streams that form a program.
Transport streams are designed to convey media (video and/or audio) signals. Other communication protocols can convey multiple information types that differ from video. These communication protocols are not tailored to carry only video and can carry video as well as other types of information. Such communication protocols are referred to as Multiple Purpose Communication Protocols (MPCPs).
Usually, communication networks use a stack of communication protocols. The seven layer OSI model includes seven layers, while other commonly used protocol stacks include a different amount of layers.
MPCP protocols are usually the lower layer protocols of a protocol stack. They may include inter-network layer protocols, network interface layer protocols, and even transport layer communication protocols that differ from the MPEG transport stream.
Some commonly used MPCP protocols are ATM, IP, UDP, Ethernet, GigaEthernet, and the like.
Media applications are time sensitive and usually do not use the TCP protocol but rather the UDP protocol. The UDP protocol is less reliable than the TCP but is not associated with the delays that characterize the TCP protocol. Each program is sent to the edge QAM modulator with a unique UDP port.
One common protocol stack includes MPEG transport stream, UDP, IP and Ethernet. Accordingly, an MPCP thread that conveys such a TS includes TS packets that are encapsulated within IP packets, UDP packets, Ethernet frames, and the like.
FIG. 1 illustrates a prior art Ethernet frame 90. Ethernet frame 90 includes an Ethernet header 91, an IP header 92, a UDP header 93, an Ethernet frame trailer 94 as well as multiple TS packets 75. An exemplary transport packet (of a TS) 75 includes transport stream payload (not shown) and a transport stream header. Various fields of the transport stream header are shown. Some are omitted for simplicity of explanation. The illustrated fields of the transport stream header include: a transport error indication bit 81, PID field 82, continuity counter field 83, discontinuity indicator field 85, and PCR field 87. The discontinuity indicator field 85 is a part of an adaptation field 84. The PCR field 87 is a part of optional fields 86.
Video On Demand systems include near video on demand, true video on demand and the like. Video on demand systems are capable of providing programs to viewers (also referred to as clients or end-users) over communication networks such the HFC network. It is noted that networks other than HFC networks can be used.
Modern video on demand systems include multiple video on demand (VOD) servers that store multiple programs, resource managers and edge QAM modulators. The edge QAM modulators usually are adapted to: (i) receive Ethernet frames that encapsulate the transport packets, (ii) de-capsulate these frames and remove network jitter, and (iii) transmit radio frequency signals representative of the transport stream packets to end users, over the HFC network.
A white paper written by NetPredict of Menlo Park, Calif., titled “Probabilistic Approach to Provisioning of Resources for Delivery of Interactive TV”, describes a forward path delivery system that allows MPEG-2 content from a headend or a remote source to be sent, over an IP network, to a remote edge QAM modulator. Edge QAM modulator performs various modulations and sends a Radio Frequency signal over a Hybrid Fiber Coax (HFC) network to 500 to 2000 end users.
A white paper written by Motorola™ titled “Next-Generation CMTS architecture: Protecting Network Investments While Migrating to Next-Generation CMTS Platforms”, which is incorporated herein by reference, describes a decoupled CMTS that includes: (i) a forwarder, (ii) a MAC domain manager, (iii) Upstream Receiver PHY, (iv) Downstream Edge QAM modulators and (v) a Gigabit Ethernet Switch Matrix. The upstream receiver PHY received upstream information from multiple clients, encapsulates the upstream packets to Ethernet frames and sends control packets to the MAC domain manager while sending data packets to the forwarder. The Forwarder routes traffic between the HFC network and an IP regional network. The traffic can be upstream data, downstream data, and downstream video on demand. In the downstream direction the forwarder sends DOCSIS traffic from the regional IP networks and sends it to the appropriate edge QAM modulator. The MAC domain manager controls access to the upstream DOCSIS channel.
The edge QAM modulator receives data packets and transport stream packets (provided to the regional IP network from a VOD server) from the forwarder, performs some packet processing and timing corrections, multiplexes downstream data and VOD MPEG streams, implements modulation, performs frequency up-conversion and transmits a radio frequency signal over the HFC.
A typical edge QAM almost does not interact with other components of the VOD network. Typically it only receives configuration (usually frequency allocation) and status reports.
One main concern of a distributed VOD system is that for various reasons a VOD server may erroneously transmit to the edge QAM modulator a program that shouldn't be provided to the edge QAM modulator and hence to the clients. Such a program can be, for example, a program with adult content that is sent to under-aged clients, or a program that was erroneously sent to the client that was not subscribed to the video on demand services.
There is a need to enhance the control of programs that are sent by the edge QAM modulator.